The present invention relates to method and apparatus of processing a distal end of an optical fiber by grinding the distal end of the optical fiber and, more particularly, to method and apparatus of processing an distal end of an optical fiber in a semi-cylindrical curved surface with a given curvature radius (namely, wedge-shaped lens).
Hereinafter, for simplicity, the above-type optical fiber with wedge-shaped lens is defined as a wedge-shaped optical fiber.
In compliance with rapid increase in the amount of communication caused by widely spread Internets, optical communication networks have been expanding at an accelerating pace, and multiplexing of wavelength has been rapidly progressing in optical transmission. In this situation, an optical fiber amplifying technology has been absolutely essential. For instance, in order to amply a light beam within a frequency band of 1.53˜1.565 μm, called C-band, an Erbium-Doped Fiber Amplifier (EDFA) has been commonly deployed. Although an excitation optical source for the EDFA has been employed a GaAs semiconductor laser diode, this laser diode has a complicated embedding structure and it is hard to alter a spot size of this laser diode.
For this reason, as shown in FIG. 1, the semiconductor laser diode 30 of this type has a horizontally extending flat opening 30a. A full divergent angle of an output beam 30b emitted outside of the opening 30a has a transverse angle of 4˜6° and a longitudinal angle of 27˜28° to provide a large aspect ratio. Therefore, an output beam pattern has an elliptical configuration largely extended in a longitudinal direction.
In order to obtain a high performance optical fiber amplifier to enable such an output beam to be efficiently injected into an optical fiber, a technology has been in use which includes processing a distal end of the optical fiber in a wedge shape with a microscopic curvature radius to allow the opening of the optical fiber to be matched with the aspect ratio of the semiconductor laser diode.
FIG. 2 is a perspective view illustrating a coupling condition between the semiconductor laser diode and a wedge-shaped optical fiber. The wedge-shaped optical fiber F is comprised of a core 2, a pair of tapered surfaces 2a, 2b, and a curvature surface 3a processed on a wedge-shaped distal end 3 formed by the pair of tapered surfaces 2a, 2b. A typical shape involves a core diameter of 3.5 μm and a tapering angle 2θ, formed by the pair of tapered surfaces 2a, 2b, of approximately 50°. The curvature surface 3a is formed in a semi-cylindrical shape, and an end face of the core 2 is exposed at a central area of the curvature surface 3a. 
Since the curvature surface 3a has a function of a cylindrical lens, allowing an output beam waist of the semiconductor laser diode 30 to be matched with a focal point of the curvature surface 3a enables the output beam 30b to be injected into the core 2 with an extremely high efficiency. Accordingly, the wedge-shaped optical fiber F is effective to be coupled to the semiconductor laser diode 30 having the flat opening 30a. 
However, since the opening 30a of the semiconductor diode 30 is extremely thin, in order to high efficiently couple the wedge-shaped optical fiber F with the semiconductor laser diode 30, there is a need for a curvature radius R of the curvature surface 3a to be controlled in an extremely small value of 3˜6 μm. Further, the deviation between a ridgeline center of the wedge-shaped distal end 3 and a core center of the core 2 must be controlled at a precision in the submicron order. That is, it is required for the pair of tapered surfaces 2a, 2b to have an extremely high geometric symmetry with respect to the core center of the core 2.
When performing accurate processing the distal end of the optical fiber in a desired form with such a high precision, subsequent to the distal end of the optical fiber being held in pressured contact with a grinding tool by a skilled person in the related art for processing, repeated operations are implemented to carry out corrective processing upon measurement by a shape measuring device or an optical characteristic measuring device.
Alternately, another attempt has been made to fixedly secure the distal end of the optical fiber on a precision stage having a rotational axis whereupon a complicated locus is accurately controlled to allow the distal end of the optical fiber to be formed into a desired shape, as disclosed in Japanese Patent Provisional Publications No. 59-97832, No. 2-42333, No. 8-271763 and No. 11-174236.